In a computer, the length of electric wiring between the power supply and the IC chip is usually long, and therefore, the loop inductance at this electric wiring is extremely large. The variation in the voltage at which the IC is driven in high-speed operation mode becomes very large accordingly, possibly causing malfunction of the IC. In addition, it becomes difficult to stabilize the voltage of the power supply. In an attempt to avoid these troubles, a capacitor is mounted on the surface of the printed circuit board as an auxiliary device for assisting the power supply operation.
Specifically, the loop inductance which causes the variation in voltage depends on the length of electric wire from a power supply shown in FIG. 72(A) to a power supply terminal 272P of an IC chip 270 through a power supply line in a printed circuit board 300, and the length of electric wire from a ground terminal 272E in the IC chip 270 to the power supply through a ground line in the printed circuit board 300 from the power supply. The loop inductance can be reduced by narrowing the distance between the electric wires through which a current in a reverse direction to each other flows, for example, the distance between the power supply line and the ground line.
Therefore, as shown in FIG. 72(B), a chip capacitor 298 is mounted on the surface of the printed circuit board 300, thereby shortening the length of electric wire between the power supply line and the ground line in the printed circuit board 300 which connects the IC chip 270 to the chip capacitor 292 to be the power supply source, as well as narrowing the distance between the electric wires.
However, the degree of the voltage drop, which causes the variation in the IC driving voltage, depends on the frequency at which the IC chip is driven. As the frequency at which the IC chip is driven increases, it becomes impossible to reduce the loop inductance even if the chip capacitor is mounted on the surface of the printed circuit board 300 as is conducted in the case shown in FIG. 72(B). As a result, it becomes difficult to sufficiently suppress the variation in the IC driving voltage.
In this situation, the present inventors have conceived to mount a chip capacitor inside the printed circuit board. As a method for embedding a capacitor into a substrate, techniques described in Japanese Unexamined Patent Publications Nos. 6-326472, 7-263619, 10-256429, 11-45955, 11-126978, 11-312868 and the like may be employed.
Japanese Unexamined Patent Publication 6-326472 discloses a technique in which a capacitor is embedded in a substrate made of resin such as glass epoxy. This structure reduces the noise in the power supply, and eliminates the need of the space for mounting the chip capacitor, thereby reducing the size of insulating substrate. Japanese Unexamined Patent Publication No. 7-263619 discloses a technique in which a capacitor is embedded into to a substrate made of ceramics or alumina. The capacitor is connected between the power supply layer and the ground layer. This structure shortens the length of electric wire and reduces the inductance of the electric wire.
However, these prior art techniques described above cannot satisfactorily shorten the distance between the IC chip and the capacitor, and also cannot reduce the inductance at the higher frequency domain of the IC chip to a level required at present. In particularly, a buildup multi-layer printed circuit board made of resin has problems such as disconnection between the terminal of the chip capacitor and the via hole, the peeling of the chip capacitor from the interlayer resin insulating layer, and the generation of cracks in the interlayer resin insulating layer, resulted from the difference in thermal expansion coefficients between the capacitor made of ceramics, and the core substrate and the interlayer resin insulating layer made of resin. These problems hinder the printed circuit board from having high reliability over a long period of time.
The present invention has been made to solve the above-described problems of the prior arts, and the objective thereof is to provide a printed circuit board capable of reducing a loop inductance and having high reliability, and a method for manufacturing the same.